Infusion device and driving mechanism and process for same with actuator for multiple infusion uses

ABSTRACT

A drive mechanism for delivery of infusion medium a coil capable of being electrically activated to provide an electromagnetic field. The coil surrounds a piston channel extending in an axial direction. An armature is located adjacent the coil, on one side of the axial channel. The armature is moveable toward a forward position, in response to the electromagnetic field produced by activation of the coil. A piston is located within the piston channel and is moveable axially within the channel to a forward position, in response to movement of the armature to its forward position. The armature and piston are moved toward a retracted position, when the coil is not energized. The armature may be configured with a reduced diameter by including a coil cup for supporting the coil including a shelf portion defining at least a portion of a pole surface of the coil cup.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Embodiments of the present invention relate to a U.S. patentapplication entitled “Infusion Device and Driving Mechanism For Same,”Ser. No. 10/033,722, filed Dec. 27, 2001, the disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates generally to infusion devices,systems and processes and, in particular embodiments to infusiondevices, systems and processes employing a drive mechanism configurationhaving an actuator configured for improved efficient operation with avariety of types of infusion media. Further embodiments of the inventionrelate to drive mechanisms for such infusion devices and systems, andprocesses of making and using such drive mechanisms.

BACKGROUND

[0003] Infusion devices are typically used to deliver infusion media,such as medication, to patients. An implantable infusion device ismedium to the patient at a regulated dosage. An external infusion deviceis designed to be located outside of the patient's body and connected tothe patient by a suitable catheter, tubing or the like, to administer aninfusion medium into the patient's body.

[0004] Both implantable and external infusion devices may include one ormore pump drive mechanisms for creating pumping forces to cause or helpdelivery of infusion media to the patients. Various types of pump drivemechanisms with electromagnetic drive devices have been developed forsuch infusion devices. Such pump drive devices typically include anelectromagnetic actuator having an armature portion made of amagnetically conductive material. The armature interacts,electromagnetically, with an electrical coil housed in a coil cup madeof magnetically conductive material. Such drive mechanisms include, forexample, the drive mechanisms described in U.S. patent applicationentitled “Infusion Device and Driving Mechanism For Same,” Ser. No.10/033,722, filed Dec. 27, 2001, by the owner of the present invention.Other pump drive mechanisms having electromagnetic armature-coilassemblies include, for example, those described in U.S. Pat. No.4,594,058 to Fischell; U.S. Pat. No. 4,684,368 to Kenyon; U.S. Pat. No.4,569,641 to Falk et al.; U.S. Pat. No. 4,568,250 to Falk, et al.; U.S.Pat. No. 4,636,150 to Falk, et al.; and U.S. Pat. No. 4,714,234 to Falket al.

[0005] Pump drive mechanisms for infusion devices (including thosereferenced above) may include components, such as actuators, that comeinto direct contact with the infusion medium during normal operation. Insuch infusion devices, the chemical interaction of the infusion mediumwith materials used for such components may have an adverse effect onthe patient to which the infusion medium is administered. The risk ofsuch an adverse effect may be greater for implantable infusion devices,where components of an infusion pump may remain in contact with infusionmedium over a prolonged period of time inside of an implanted device.For example, contact with the armature may cause leaching or otherinteractions of materials between the infusion medium and the armature.Such interactions may adversely alter the medical effect of the infusionmedium on the patient. Prolonged contact may cause other detrimentaleffects, such as corrosion of the armature.

[0006] Pump drive mechanisms may be manufactured for use with aparticular, known infusion medium, in which case, the effect (andprolonged effect) of direct contact of that particular infusion mediumon components of the pump drive mechanism may be studied in advance.With such studies, the materials and components of the infusion pump maybe selected and designed to be in contact with the infusion medium, yet,have a suitably benign effect on the patient. However, if the particulartype of infusion medium is not known at the time of manufacture of thepump mechanism, for example, in the case in which a pump mechanism isbeing manufactured for multiple possible infusion uses, the ability tostudy effects on all possible infusion media may not be practical orpossible. Accordingly, there is a demand in the industry for a pumpmechanism and process that is suitable for multiple possible infusionuses.

[0007] In some contexts of use, the infusion device must be operable foran extended period with a limited power supply. For example, batterypowered infusion devices may be implanted in or otherwise connected topatients, to deliver medication at controlled intervals over a prolongedperiod of time. A battery replacement in an implanted device may requiresurgery on the patient to remove and re-implant the device. Accordingly,there is a demand in the industry for infusion devices which makeefficient use of power supplies and, thus, require fewer or no powersupply replacements.

[0008] Because implantable infusion devices are designed to be implantedin the patient's body, the dimensions of such devices can have an impacton the determination of the location in the body at which a device maybe implanted, the level of comfort of the implant patient and theexternal appearance of the implant site. Typically, a device withrelatively small dimensions and, in particular, a relatively smallthickness form factor, will provide greater flexibility in the choice oflocation in the patient's body to place the implant and will minimizepatient discomfort and minimize noticeable protrusions at the implantsite. Accordingly, there is a demand in the industry for minimizing theoverall dimensions, and, in particular, the thickness dimension ofimplantable infusion device.

[0009] Summary of the Disclosure

[0010] Accordingly, embodiments of the present invention relate toinfusion devices and drive mechanisms for infusion devices which addressone or more of the above-mentioned industry demands.

[0011] Embodiments of the invention relate to such devices and drivemechanisms configured for use with any one of multiple differentinfusion media.

[0012] Further embodiments relate to such devices and drive mechanismsconfigured and operated to make highly efficient use of electrical powerto prolong operational life.

[0013] Further embodiments of the invention relate to such devices anddrive mechanisms configured for implantation in a patient's body and,thus, configured to have a relatively small thickness dimension, forexample, to minimize trauma to the implant recipient (referred to hereinas the patient). However, aspects of the invention may apply to externalinfusion devices and drive mechanisms for such external devices and,thus, other embodiments of the invention relate to such externalinfusion devices and drive mechanisms.

[0014] An implantable infusion device according to an embodiment of theinvention includes a housing made from a biocompatible and infusionmedium compatible material. The infusion device housing contains areservoir for holding a volume of infusion medium, such as, but notlimited to, a medication to be administered to the patient. The infusiondevice housing has an outlet through which the infusion medium may beexpelled.

[0015] The infusion device further includes a drive mechanism having aninlet coupled in fluid flow communication with the reservoir and anoutlet coupled in fluid flow communication with the infusion devicehousing outlet. The drive mechanism employs electromagnetic andmechanical forces to move an actuator piston between retracted andforward positions or states, to cause infusion medium to be drawn fromthe reservoir, through an inlet and forced out of an outlet.

[0016] A drive mechanism, according to one embodiment, comprises anassembly of components which may be manufactured and assembled in arelatively cost efficient manner. The components include a housingcontaining a coil disposed within a coil cup and a piston channelsurrounded by the coil. The components also include an actuator having apiston extending through the piston channel and an armature disposed atone end of the piston channel. A piston chamber, outlet chamber andoutlet valve are located at the other end of the piston channel.

[0017] According to embodiments of the present invention, the coil cupmay be composed of a magnetizable material and may include a generallyannular outer wall, the outer wall having a generally annular shelfportion extending from the outer wall towards the inner wall. The shelfportion has an end defining an outer pole surface of the coil cup. Inone embodiment of the present invention, the inner wall of the coil cupincludes a generally annular shelf portion extending from the inner walltowards the outer wall. The shelf portion has an end defining at least aportion of an inner pole surface of the coil cup. The coil cup includesa generally annular interior between the outer and inner walls. Theannular interior contains a coil.

[0018] When the coil is in a quiescent state, the armature and pistonare urged toward a retracted position by mechanical or magnetic forces.When the coil is energized, the armature and piston move to a forwardstroke position. The movement of the piston from a retracted position toa forward position creates pressure differentials within the drivemechanism to drive medium out the outlet. Mechanical force may returnthe piston to the retracted position. The movement of the piston from aforward position to a retracted position creates pressure differentialsto draw medium into the drive mechanism inlet and into the pistonchamber.

[0019] Various types of electromagnetic actuator type drive mechanismsfor infusion devices have been configured with actuators having anarmature portion made of a magnetically conductive material. Thearmature interacts, electromagnetically, with an electrical coil housedin a coil cup made of magnetically conductive material. An example of apump drive mechanism suitable for an implantable infusion device isdescribed in U.S. patent application entitled “Infusion Device andDriving Mechanism For Same,” Ser. No. 10/033,722, filed Dec. 27, 2001,by the owner of the present invention. Certain embodiments of thepresent invention include a pump drive mechanism as described in U.S.patent application Ser. No. 10/033,722, but with differences relating tothe actuator and/or coil cup configuration and operation as describedherein. Other embodiments may employ other suitable pump drivemechanisms having actuator and/or coil cup aspects as described herein.

[0020] As described in further detail below, armature portions ofactuators employed in embodiments of the present invention may beconfigured with a reduced diameter, for example, to reduce fluidicresistance to actuator movement. Alternatively, or in addition, furtherembodiments of the present invention employ an armature structure thatis free of apertures (or employs a reduced number of apertures ascompared to actuators described in U.S. patent application Ser. No.10/033,722) and, thus, may be provided with a protective layer orcoating in a simplified manufacturing process.

[0021] Other embodiments may employ an armature that may be manufacturedfrom any suitable material, including materials having a low magneticpermeability. According to these embodiments, the armature portion ofthe actuator may be formed with a cavity into which a material having arelatively high magnetic permeability may be placed. These materials maybe, for example, ferrous materials.

[0022] Alternatively, or in addition, actuators according to furtherembodiments of the invention employ a piston portion that has a centralchannel and valve structure for increasing the flow rate of infusionmedium into a pumping chamber and inhibiting backflow of infusion mediumfrom the pumping chamber. In yet further embodiments, the diameter ofthe piston portion may be reduced and/or the diameter of the pistonchannel in which the piston moves may be increased, to increase the flowrate of infusion medium into the pumping chamber. By accommodating anincreased flow rate, the drive mechanisms may be operable with a greatervariety of infusion media.

[0023] Embodiments of the invention may employ a coaxial arrangement ofthe piston, the piston channel and the coil, to provide significantadvantages with respect to providing a relatively thin form factor andefficient power usage. A number of features described herein and in U.S.patent application Ser. No. 10/033,722 can each provide or be combinedto contribute to a reduction in the thickness form factor of the drivemechanism. For example, a coaxial arrangement of components can beimplemented with a smaller thickness form factor than alternativearrangements in which components are arranged in series with each otherin the thickness dimension. Embodiments may include an inlet volume orchamber on one side of the coil and an outlet chamber on the oppositeside of the coil, with a flow passage through the piston channel, suchthat the coil and flow channel share a common portion of the thicknessdimension. The armature may be located within the inlet volume and,thus, share a common portion of the thickness dimension with the inletvolume. The outlet chamber may be centrally located within the samehousing that has the coil cup and formed in relatively close proximityto the coil cup in the thickness dimension of the housing.

[0024] In addition, a number of features described herein and in U.S.patent application Ser. No. 10/033,722 can provide, or be combined tocontribute to, the efficient use of power to, prolong the operationallife of the drive mechanism.

[0025] These and other aspects and advantages of the invention will beapparent to one of skill in the art from the accompanying detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Referring now to the drawings in which like reference numbersrepresent corresponding parts throughout:

[0027]FIG. 1 is a perspective view of an implantable infusion deviceaccording to an embodiment of the invention.

[0028]FIG. 2 is a perspective view of a drive mechanism for animplantable infusion device according to an embodiment of the invention.

[0029]FIG. 3A is a cross-section view of one example embodiment of thedrive mechanism of FIG. 2, in a retracted position or state.

[0030]FIG. 3B is a cross-section view of one example embodiment of thedrive mechanism of FIG. 2, in a retracted position or state.

[0031]FIG. 3C is a cross-section view of one example embodiment of thedrive mechanism of FIG. 2, in a retracted position or state.

[0032]FIG. 3D is a cross-section view of one example embodiment of thedrive mechanism of FIG. 2, in a retracted position or state.

[0033]FIG. 4A is a cross-section view of the example drive mechanismembodiment of FIG. 3A, in a forward stroke position or state.

[0034]FIG. 4B is a cross-section view of the example drive mechanismembodiment of FIG. 3B, in a forward stroke position or state.

[0035]FIG. 4C is a cross-section view of the example drive mechanismembodiment of FIG. 3C, in a forward stroke position or state.

[0036]FIG. 4D is a cross-section view of the example drive mechanismembodiment of FIG. 3D, in a forward stroke position or state.

[0037]FIG. 5 is a an exploded view of an embodiment of the drivemechanism shown in FIGS. 3A-D and 4A-D.

[0038]FIG. 6 is a perspective view of an embodiment of a housing memberfor the drive mechanism in FIGS. 3A-D and 4A-D.

[0039]FIG. 7A is a perspective view of an embodiment of a coil cup forthe drive mechanism having an outer shelf.

[0040]FIG. 7B is a perspective view of an embodiment of a coil cup forthe drive mechanism having an inner shelf.

[0041]FIG. 7C is a perspective view of an embodiment of a coil cup forthe drive mechanism having both an outer and inner shelf.

[0042]FIG. 8 is a perspective view of an embodiment of an actuatorcomprising an armature and a piston for the drive mechanism in FIGS.3A-D and 4A-D.

[0043]FIG. 9 is a simplified cross-section diagram, showing anarrangement of an actuator member and coil cup member for the drivemechanism in FIG. 3A.

[0044]FIG. 10 is a simplified cross-section diagram, showing anotherembodiment of an actuator comprising an armature and a piston for adrive mechanism of the type shown in FIGS. 3A-D and 4A-D.

[0045]FIG. 11 is a simplified cross-section diagram, showing anotherembodiment of an actuator comprising a 2-piece structure having anarmature and a piston, for a pump drive mechanism.

[0046]FIG. 12 is a simplified cross-section diagram, showing yet anotherembodiment of an actuator comprising an armature and a piston for adrive mechanism of the type shown in FIGS. 3A-D and 4A-D and including avalve structure on one end of the piston.

[0047]FIG. 13 is a detailed view of an embodiment of a valve structureshown in FIG. 12.

[0048]FIG. 14A is a simplified cross-section diagram, showing anunassembled armature according to embodiments of the present invention.

[0049]FIG. 14B is a simplified cross-section diagram, showing anassembled armature according to embodiments of the present invention.

[0050]FIG. 15 is a simplified cross-section diagram, showing anassembled actuator including an armature and a piston, according toembodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0051] The following detailed description is of the best presentlycontemplated mode of implementing the invention. This description is notto be taken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of embodiments of the invention. Thescope of the invention is best defined by the appended claims.

[0052] As discussed above, the present invention relates generally toinfusion devices having drive mechanisms and also to drive mechanismconfigurations for infusion of a medium into a patient or otherenvironment. Embodiments of the invention relate to such devices anddrive mechanisms configured for use with any one of multiple differentinfusion media.

[0053] Embodiments of the invention relate to such devices and drivemechanisms configured for implantation in a patient's body. Embodimentsdescribed herein allow the drive mechanism for such infusion device tohave a relatively small thickness dimension, for example, to minimizetrauma to the implant recipient (referred to herein as the patient).Further preferred embodiments relate to such devices and drivemechanisms configured and operated to make highly efficient use ofelectrical power to prolong operational life in an implant environment.However, because aspects of the invention may be applied to externalinfusion devices as well, yet further embodiments of the inventionrelate to such external infusion devices and drive mechanisms for suchexternal devices.

[0054]FIG. 1 shows an implantable infusion device 10 according to anembodiment of the invention. The illustrated device 10 is configured tobe surgically implanted into a patient, for example, in the abdominalregion, between the skin and the abdominal wall. A catheter connected tothe pump may deliver infusion medium to the patient, for example, byfeeding infusion medium to a particular location in the venous system,in the spinal column, in the peritoneal cavity, or in another suitablelocation of the patient.

[0055] Preferred embodiments of the device 10 are configured inaccordance with one or more aspects of the invention for enhancingoperability with multiple types of infusion media, enhancing power usageefficiency and simplifying implantation. As noted above, furtherembodiments of the invention may be implemented as external infusiondevices, which connect to patients through suitable catheter devices orthe like. Yet further embodiments of the invention may be used in othercontexts, for delivery of a medium into other suitable environments.Therefore, for purposes of simplifying the present disclosure, the term“patient” is used herein to refer to the entity or environment in whichan implantable device is implanted or to which an external device isconnected, whether or not the implant or connection is carried out formedical purposes. Also, the term “infusion medium” is used herein torefer to any suitable medium delivered by the drive device.

[0056] The device 10 in FIG. 1 includes a generally disc-shaped housing12. While a generally circular disc-shaped embodiment is illustrated inFIG. 1, further embodiments of the invention may employ housings ofother shapes, including, but not limited to, oval, oblong, rectangular,or other curved or polygonal shapes. The housing 12 has a diameterdimension D, defining the diameter of the disc shape, and a maximumthickness dimension T, defining the maximum thickness of the device.

[0057] In implantable device embodiments, the housing 12 preferably ismade of a biocompatible material, is hermetically sealed from theexternal environment and has a relatively small or minimized thicknessdimension T, to reduce or minimize patient trauma during implant surgeryand after implantation. For example, the housing 12 may be made fromtitanium, titanium alloy, stainless steel or other biocompatiblematerials and may be configured to provide a hermetically sealedenvironment for some or all of the components within the interior of thehousing.

[0058] The housing 12 includes a reservoir housing portion 13 containinga reservoir for holding a volume of infusion medium, such as, but notlimited to, a liquid medication to be administered to the patient. Thehousing 12 includes a further housing portion 14, located above thereservoir housing portion 13 in the orientation shown in FIG. 1, forcontaining a drive mechanism 20, a power source and control electronics22 described below.

[0059] Representative examples of reservoir housing portions andreservoirs which may be employed in embodiments of the invention aredescribed in co-pending U.S. patent application Ser. No. 10/033,377(attorney docket no. 047711.0287), titled “Implantable Infusion DeviceAnd Reservoir For Same,” which is incorporated herein by reference.However, further embodiments may employ other suitable reservoirconfigurations, including, but not limited to, those described in U.S.Pat. No. 5,514,103 and U.S. Pat. No. 5,176,644, each to Srisathapat etal, U.S. Pat. No. 5,167,633 to Mann et al., U.S. Pat. No. 4,697,622 toSwift and U.S. Pat. No. 4,573,994 to Fischell et al.

[0060] The housing 12 also has an outlet 16 through which the infusionmedium may be expelled. When the device 10 is implanted in a patient orconnected externally to a patient, a catheter may be connected to theoutlet 16, to deliver infusion medium expelled from the outlet 16 intothe patient's blood stream or to a selected location in the patient'sbody. The infusion device 10 may also include an inlet structure 18which provides a closeable and sealable fluid flow path to the reservoirin the reservoir portion 13 of the housing. In an example embodiment,the inlet structure provides a port for receiving a needle through whichfluid may be transferred to the infusion device, for example, to fill orre-fill the reservoir of the device. The inlet structure may beconfigured to re-seal after a fill or re-fill operation, to allowmultiple re-fill and re-seal operations.

[0061] One example of an inlet structure is described in co-pending U.S.patent application Ser. No. 10/034,628 (attorney docket no.047711.0286), titled “Infusion Device And Inlet Structure For Same,”which is incorporated herein by reference. However, further embodimentsmay employ other suitable inlet structures, including, but not limitedto, those described in U.S. Pat. No. 5,514,103 and U.S. Pat. No.5,176,644, each to Srisathapat et al, U.S. Pat. No. 5,167,633 to Mann etal., U.S. Pat. No. 4,697,622 to Swift and U.S. Pat. No. 4,573,994 toFischell et al.

[0062] As described above, preferred embodiments of the device 10 areconfigured in accordance with one or more aspects of the invention forenhancing operability with multiple types of infusion media. In suchembodiments, any one of various types of infusion media having differentcompositions, concentrations and/or chemical characteristics may becontained, filled or re-filled into the reservoir for a given infusiontreatment program. Thus, in such embodiments, the components of thereservoir, inlet and outlet structures that come into contact with theinfusion medium may be made with (or coated with) a suitable materialthat will minimize the risk of having an adverse reaction with a any ofthe multiple types of infusion media that may be contained in thereservoir. Suitable materials may include, but are not limited to,titanium, titanium alloy, stainless steel or the like.

[0063] The infusion device 10 includes a drive mechanism 20, such as apump, and an electronic control system 22 located in the housing portion14. The drive mechanism 20 is connected between the reservoir and theoutlet 16. The electronic control system 22 includes a power source,such as a battery, and control electronics for controlling the drivemechanism 20 to deliver infusion medium from the reservoir, to thepatient in a selected manner. The drive mechanism may be controlled todeliver infusion medium in any suitable manner, for example, accordingto a programmed dispensing rate or schedule, according to an actuationsignal from a sensor, timer, manual actuator or other suitable source,or combinations thereof.

[0064] The programmed dispensing rate or schedule may be different fordifferent types of infusion media. Thus, the control system 22 mayinclude programmable electronics which allow programming of dispensingfunctions, including rate, schedule, dispensing time, dispensing period,sensor activities that trigger dispensing and the like, depending uponthe type of infusion medium contained in the reservoir. Such programmingmay be accomplished prior to implantation. In other embodiments,programming may be accomplished by a wireless communication link, afterimplantation. Systems for wireless communication between controlelectronics of an implanted infusion device and an external programmingdevice are described in U.S. patent application Ser. No. 10/033,530,titled “Safety Limits for Closed-Loop Infusion Pump Control”, filed Dec.26, 2001, which is owned by the owner of the present invention.

[0065] An example of a pump drive mechanism suitable for an implantableinfusion device is described in U.S. patent application entitled“Infusion Device and Driving Mechanism For Same,” Ser. No. 10/033,724,filed Dec. 27, 2001, by the owner of the present invention andincorporated herein by reference. Certain embodiments of the presentinvention include a pump drive mechanism 20 similar to that described inU.S. patent application Ser. No. 10/033,722, but with differencesrelating to the actuator and/or coil cup configuration and operation asdescribed herein. Other embodiments may employ other suitable pump drivemechanisms having actuator and/or coil cup aspects as described herein.

[0066] The pump drive mechanism described in U.S. patent applicationSer. No. 10/033,724 employs an actuator having an armature portion thatis formed with a plurality of apertures and radial rib sections. Theapertures allow the armature portion to move in a volume of fluidicinfusion media, with reduced fluidic resistance. This is accomplished,by allowing infusion media to pass through the apertures as the armatureportion moves back and forth between forward and retracted positions.The radial ribs provide radial paths for electromagnetic flux betweenthe pole surfaces of the armature. However, an armature structure thathas a plurality of apertures and radial rib portions may be difficult tolayer with a protective material or coating. It can be difficult tolayer or apply coatings to all exposed surfaces formed by the aperturesand ribs.

[0067] Accordingly, embodiments of the present invention employ anarmature structure that is free of apertures (or employs a reducednumber of apertures as compared to actuators described in U.S. patentapplication Ser. No. 10/033,722) and, thus, may be readily provided witha protective layer or coating in a simplified manufacturing process.Such armature portions may be configured with a reduced diameter, forexample, to reduce fluidic resistance to actuator movement. Furtherembodiments of the invention employ an armature structure with apertures(as described in U.S. patent application Ser. No. 10/033,722), but witha reduced diameter, for example, to reduce fluidic resistance to motionand improve power usage efficiency.

[0068] Alternatively, or in addition, actuators according to furtherembodiments of the invention employ a piston portion that has a centralchannel and valve structure for increasing the flow rate of infusionmedium into a pumping chamber and inhibiting backflow of infusion mediumfrom the pumping chamber. In yet further embodiments, the diameter ofthe piston portion may be reduced and/or the diameter of the pistonchannel in which the piston moves may be increased, to increase the flowrate of infusion medium into the pumping chamber. By accommodating anincreased flow rate, the drive mechanisms may be operable with a greatervariety of infusion media.

[0069] The drive mechanism 20 includes mechanical and electromagneticcomponents that inherently inhabit a volume of space within the housing12. In that regard, the drive mechanism 20 can contribute to thethickness requirements of the housing 12 and, thus, to the overallthickness dimension T of the device 10. Preferred embodiments of thepresent invention relate to and employ drive mechanism configurationsthat reduce or minimize the thickness requirements of the device,without compromising drive capabilities.

[0070] The above-referenced U.S. patent application Ser. No. 10/033,722describes features relating to the ability to reduce or minimize thedevice thickness dimension T, without compromising the drivecapabilities. Such features can provide significant advantages withrespect to patient comfort, appearance and flexibility in selectingimplant locations in the body. Embodiments of the present invention mayemploy one or more of such features, in conjunction with other aspectsof the actuator and coil cup configurations described herein forimproving operation with any one of multiple types of infusion media inan implant environment.

[0071] Also in further embodiments, the device 10 is configured suchthat, once implanted, it functions for a relatively long period of timeto administer infusion medium to the patient and periodically bereplenished from outside of the patient's body. The operational life ofthe device 10 is, however, limited in part by the capacity of its powersource and the power requirements of the device. Preferred embodimentsof the device 10 employ drive mechanisms, as described below, thatprovide reliable pumping action and are highly efficient with respect topower consumption, to improve the operational life of the device 10.Alternatively or in addition, drive mechanisms that provide highlyefficient use of power, as described below, may be operated with smallerpower sources (for example, smaller batteries) which can allow thedevice 10 to be made smaller.

[0072] One manner of lowering the power consumption requirements of thedevice 10 is to employ a coaxial coil and piston pump configuration andone or more features described herein and in U.S. patent applicationSer. No. 10/033,722, for making highly efficient use of electromagneticenergy. Another manner of lowering the power consumption requirements ofthe device 10 is to reduce the number of operations of the drivemechanism 20 required over a given period of time, by pumping reducedvolumes of a higher concentration infusion medium (an infusion mediumwith a higher concentration of active ingredients) or pumping higherconcentration volumes at reduced intervals. However, higherconcentration mediums may require a greater precision in controlling thevolume delivered to the patient during a drive operation, to avoiddelivering too great or too small of a volume of the higherconcentration medium to the patient. Accordingly further preferred drivemechanisms 20 are configured with one or more features described hereinto allow delivery of controlled volumes of infusion medium and, thus, toallow sufficiently precise delivery of relatively high concentrationinfusion medium.

Drive Mechanism Embodiment

[0073]FIG. 2 shows a drive mechanism 20 according to an exampleembodiment of the present invention. In the illustrated embodiment, theexample drive mechanism 20 has a partially cylindrical, disc-shapedconfiguration with an inlet 26 and an outlet 28. The inlet 26 may beconnected in flow communication with the reservoir portion 13 of thedevice 10 in FIG. 1, though suitable conduit (not shown) within thedevice 10. Similarly, the outlet 28 may be connected in flowcommunication with the outlet 16 of the device 10 in FIG. 1, throughsuitable conduit (not shown) within the device 10.

[0074] FIGS. 3A-D shows cross-sectional views of embodiments of thedrive mechanism 20, in a retracted position or state. FIGS. 4A-D showcross-sectional views of the same drive mechanism 20 embodiment, in aforward position or state. As described in more detail below, the drivemechanism 20 employs electromagnetic and mechanical forces to change (ormove) between retracted and forward states, to cause infusion medium tobe drawn in through the inlet 26 and forced out of the outlet 28.

[0075] The drive mechanism 20, according to one embodiment, comprises anassembly of components as shown in an exploded view in FIG. 5. Suchcomponents include a housing member 30, a coil cup 32, an electricallyconductive coil 34, an actuator member 36, a cover member 38 and variousother components that are described in further detail below. Some ofthose components are also shown in perspective views in FIGS. 6-8 andare described in more detail below.

[0076] The pump drive mechanisms 20 described herein may include, forexample, various components that correspond in structure and operationto similar components of the drive mechanism described in U.S. patentapplication entitled “Infusion Device and Driving Mechanism For Same,”Ser. No. 10/033,722, filed Dec. 27, 2001, by the owner of the presentinvention. However, pump drive mechanisms 20 described herein employunique configurations relating to the actuator member 36, coil cupmember 32 and related components. Such unique component configurationsmay be employed, for example, to improve the ability of the pump drivemechanism to operate with any one of a variety of types of infusionmedia, to minimize fluid stirring and fluidic resistance to actuatormotion during a pump stroke and/or to simplify manufacturing processes.

[0077] While certain embodiments of the present invention employ a pumpmechanism that is configured similar in many respects to pump mechanismsdescribed in U.S. patent application Ser. No. 10/033,722, aspects of thepresent invention may be applicable to other pump mechanismconfigurations that employ an actuator and coil cup arrangement.Accordingly, other embodiments may employ other suitable pump mechanismconfigurations.

[0078] Housing Member for Drive Mechanism

[0079] The housing member 30 according to an example embodiment of theinvention (shown in perspective view in FIG. 6) is open on one side to ahollow, annular interior section 40. The housing member 30 has a centralhub portion 42 with a central piston channel 44. The bottom side of thehousing member 30 (with reference to the orientation shown in FIGS. 3A-Dand 4A-D), includes an opening 46 to the hollow interior section 31,through which coil wires or connection leads may pass. The bottom sideof the housing member also includes a configuration of recesses andcavities for providing an outlet chamber (48 in FIGS. 3A-D and 4A-D), anoutlet passage and, in some embodiments, accumulator-chambers asdescribed in the above-referenced U.S. patent application Ser. No.10/033,722. The housing member 30 is preferably made of a generallyrigid, biocompatible and infusion medium compatible material, having noor low magnetic permeability such as, but not limited to, titanium,stainless steel, biocompatible plastic, ceramic, glass or the like.

[0080] Coil Cup Member for Drive Mechanism

[0081] As shown in FIGS. 3A-D and 4A-D, the coil cup member 32 islocated within the annular interior section of the housing 30.Perspective views of example embodiments of a coil cup 32 are shown inFIGS. 7A, 7B and 7C. The example coil cup member 32 has a generallycylindrical shape, with an opening 50 one side to a hollow, annularinterior. The coil cup member 32 includes a central hub portion 51having a central channel or bore 52 located axial relative to theannular interior. The hub portion 51 of the coil cup member defines anend surface 54 (or inner pole surface).

[0082] The coil cup member 32 has an outer peripheral wall 56 connectedto the hub portion 51 by a backiron portion 57 of the coil cup member.In the embodiment illustrated in FIG. 3A and FIG. 7A, the coil cupmember 32 also includes an annular lip or shelf 58 that extends from theouter wall 56, toward the hub portion 51, to cover a portion of thehollow interior of the coil cup member. The annular opening 50 isprovided between the hub 51 and an annular, free edge of the shelf 58.The shelf 58 has a surface 59 (or outer pole surface) facing away (andupward in FIG. 7A) from the hollow interior of the coil cup member 32.As described below, the shelf 58 allows the actuator 36 to be configuredwith a relatively small diameter armature portion. By minimizing thediameter of the armature portion, the configuration of the armature maybe simplified, thus simplifying manufacturing processes, stirring ofinfusion media during actuator movement may be reduced and the powerusage for moving the actuator may be more efficient.

[0083] In an alternative embodiment illustrated in FIG. 7B, the coil cupmember 32 may include an annular lip or shelf 98 that extends from thehub portion 51 toward the outer wall 56. The annular opening 50 isprovided between the annular, free edge of the shelf 98 and the outerwall 56. The shelf 98 has a surface 99 (extending the inner pole surface54 (see FIG. 7A)) facing away (and upward in FIG. 7B) from the hollowinterior of the coil cup member 32. The embodiment of the coil cupmember 32 shown in FIG. 7B may be employed with an actuator member asdescribed in U.S. patent application Ser. No. 10/033,722. Thus, whilethere is no reduction in the diameter of the armature structureaccording to this embodiment, shelf 98 provides a larger pole area ofthe coil cup member 32. to increase electromagnetic flux between thepole surfaces of the coil cup member 32 and the pole surfaces of thearmature.

[0084] In an alternative embodiment illustrated in FIG. 3B and FIG. 7C,the coil cup member 32 may include both an annular lip or shelf 58 thatextends from the outer wall 56, toward the hub portion 51 and an annularlip or shelf 98 that extends from the hub portion 51 toward the outerwall 56. The annular opening 50 is provided between the annular, freeedge of the shelf 98 and the annular, free edge of the shelf 58. Theshelf 58 has a surface 59 (or outer pole surface) facing away (andupward in FIG. 7C) from the hollow interior of the coil cup member 32.The shelf 98 has a surface 99 (extending the inner pole surface 54 (seeFIG. 7A)) facing away (and upward in FIG. 7C) from the hollow interiorof the coil cup member 32. The addition of shelves 58 and 98 providesthe advantages described above regarding FIGS. 7A and 7B.

[0085] In the embodiments of the present invention shown in FIGS. 3A and3B, the minimum amount of spacing that may be provided between the outerand inner poles is determined by the distance between the outer andinner poles where fringing occurs, i.e., where the electromagnetic fluxmay bridge the gap between the inner and outer poles. Thus, although itis desirable to increase the areas of the poles, a minimum distance orgap must be maintained between the inner and outer poles to avoidfringing. The large surface area of the straight edges of the inner andouter poles that are opposed one to another may increase the likelihoodthat fringing will occur for a particular spacing between the inner andouter poles. This is because the straight edges have a large amount ofsurface area over which fringing may occur.

[0086] Thus, according to further embodiments of the present inventionillustrated in FIGS. 3C and 3D, the inner edges of shelves 58 and 98 maybe angled in order to minimize the straight surface area of the innerand outer poles that are opposed one to another in order to reduce thepossibility that electromagnetic flux will bridge the gap between theinner and outer poles. Thus, a smaller gap between the inner and outerpoles may be achieved.

[0087]FIG. 3C shows the shelf 58 of FIG. 3A with an angled edge. FIG. 3Dshows the shelves 58 and 98 of FIG. 3B with angled edges. The edges maybe formed at any suitable angle. According to embodiments of the presentinvention, the angle of the edge may be between approximately 10 degreesand 20 degrees. In the embodiment shown in FIG. 3D either or both of theshelves may have angled edges.

[0088] The coil cup member 32, including the shelf 58 and/or 98, ispreferably made of a generally rigid material, having a relatively highmagnetic permeability such as, but not limited to, low carbon steel,iron, nickel, ferritic stainless steel, ferrite, other ferrousmaterials, combinations thereof, or the like. As described in furtherdetail below, at the open end of the cup member, the surfaces 54 and 59of the hub 51 and shelf 58 (FIG. 7A) and/or surfaces 54 and 99 of thehub 51 and shelf 98 (FIG. 7B) define pole surfaces that cooperate withpole surfaces on an armature to provide a path for electromagnetic fluxduring a forward stroke of the drive mechanism.

[0089] The shelf 58 (and/or 98) of the coil cup member 32 may be formedas a separate, annular element, that is secured to outer wall 56 (and/orhub 51) of the coil cup member 32 by any suitable means, including, butnot limited to, interference fitting, adhesive, welding, brazing or thelike. By forming the shelf 58 (and/or 98) separately, the manufacturingstep of placing the coil 34 in the coil cup member 32 may be simplified,because the coil 34 may be placed within the interior of the coil cupmember 32, before the shelf 58 (and/or 98) is secured to the outer wall56 (and/or hub 51). Alternatively, the shelf 58 (and/or 98) may beformed as a unitary body with the rest of the coil cup member 32, forexample, in a molding or machining process.

[0090] When assembled in the pump drive mechanism, the coil cup member32 is located in the hollow interior of the housing member 30, with thecentral hub portion 42 of the housing 30 extending through the centralchannel 52 of the coil cup 32, as shown in FIGS. 3A-D and 4A-D. The coil34 is located within the hollow, annular interior of the coil cup member32, and is disposed around the axis A of the annular interior of thecoil cup member 32. The coil cup member 32 is provided with an opening60, through which coil leads extend, as shown in FIGS. 3A-D and 4A-D.

[0091] The coil 34 comprises a conductive wire wound in a coilconfiguration. The coil wire may comprise any suitable conductivematerial such as, but not limited to, silver, copper, gold or the like,with each turn electrically insulated from adjacent turns and thehousing. In one preferred embodiment, the coil wire has a square orrectangular cross-section, to allow minimal space between windings,thereby to allow a greater number of coil turns and, thus, improvedelectrical efficiency.

[0092] A biocompatible and infusion medium compatible barrier 61 may belocated over the open side of the coil cup 32, between the armatureportion 62 and the coil cup member 32, to maintain a gap between thosetwo members and/or to help seal the annular interior of the coil cup andcoil 34. In other embodiments in which infusion medium may contact thecoil, the barrier 61 may be omitted.

[0093] Actuator Member for Drive Mechanism

[0094] A perspective view of an example embodiment of an actuator member36 for the drive mechanism 20 is shown in FIG. 8. Other exampleembodiments of actuator members are described below with reference toFIGS. 10-12. The actuator member 36 shown in FIG. 8 is configured tooperate with a coil cup member 32 having a shelf portion 58 (and/or 98)such as described above with respect to the example embodiments of FIGS.7A, 7B and 7C. However, actuator member embodiments described below withrespect to FIGS. 10-12 may be configured either to operate with a coilcup member 32 having a shelf portion 58 (and/or 98) as described abovewith respect to FIGS. 7A, 7B and 7C, or with a coil cup memberconfiguration having no shelf portion as described in theabove-referenced U.S. patent application Ser. No. 10/033,724.

[0095] With reference to the example embodiment shown in FIG. 8, theactuator member 36 has an armature portion 62 and a piston portion 64.In the example embodiment of FIG. 8, the armature portion 62 and thepiston portion 64 of the actuator are fixed together and may be formedas a single unitary actuator structure. However, other actuatorembodiments described below (with respect to FIG. 11) may employ apiston portion that is separable from the armature portion. As shown inFIG. 8, the armature portion 42 of the actuator member has a generallyround, disc shaped configuration, with an annular outer section (orouter pole) 66 and an annular inner section (or inner pole) 65. The areaof the inner and outer pole surfaces may be selected for optimalefficiency. For example, the inner pole surface area may be about0.02937 square inches, while the outer pole surface area may be about0.05347 square inches. Other embodiments may employ other suitable polesurface areas.

[0096] As described in more detail below, the armature portion 62cooperates with the pole surfaces 54, 59 and/or 99 of the coil cupmember 32, to provide a flux path for electromagnetic flux. In addition,the armature portion 62 of the actuator 36 is located in a volume of thepump mechanism 20, in which it is in direct contact with infusion mediumto be pumped to the patient. Accordingly, the armature portion 62 of theactuator 36 is preferably made of a generally rigid material, having arelatively high magnetic permeability such as, but not limited to,ferrous materials such as S44700 stainless steel (ASTM A276-98b) or thelike.

[0097] In addition, in preferred embodiments, the ferrous material ofthe armature portion 62 is suitably covered with a biocompatible andinfusion medium compatible material, such as titanium or titanium alloycladding. Titanium can exhibit a relatively high level of corrosionresistance and compatibility with a large variety of infusion media.Accordingly, embodiments of the invention may employ a titanium ortitanium alloy coating on the armature portion (and other portions ofthe pump drive mechanism that come into direct contact with the infusionmedium), to allow operation with any one of a variety of different typesof infusion media. For example, embodiments of the invention may employa layer of about 1.5 mils to about 3.0 mils of titanium or titaniumalloy on a ferrous armature portion 62. However, other embodiments mayemploy other suitable cladding thicknesses and other suitable coatingmaterials that provide a sufficient resistance to and compatibility witha variety of types of infusion media, including, but not limited to,carbon coating, gold, platinum, diamond, titanium nitride or otherceramic material. Such coatings may be applied in any suitable manner,including, but not limited to electrochemical or electromagneticdeposition, dipping or applying liquid cladding materials that solidifyon the actuator, or the like.

[0098] In one example embodiment (not shown), the armature portion 62 ofthe actuator member 36 is provided with a plurality of apertures andradial struts as described in further detail in the above-referencedU.S. patent application Ser. No. 10/033,722. Such apertures allow thearmature portion of the actuator to move within a volume of fluidicinfusion media with reduced resistance from the fluid (by allowing fluidto pass through the apertures during actuator movement). The radialstruts complete the flux path between the inner and outer poles of thearmature portion 62.

[0099] However, such apertures and struts in the armature portion canincrease the manufacturing complexity, especially if the magneticallypermeable material of the armature portion 62 is to be clad with atitanium, titanium alloy or other suitable cladding material. Inparticular, it can be difficult to sufficiently clad all exposedsurfaces of an armature portion having such apertures and radial struts.Accordingly, further embodiments employ an armature portion 62 that isfree of apertures and radial struts. Yet other embodiments employ arelatively small number of apertures.

[0100] Without apertures (or with a reduced number of apertures), theproblems associated with fluidic resistance and stirring of the infusionmedia noted above may be encountered. Accordingly, embodiments employingarmature portions 62 with no or minimal apertures are preferablyconfigured with a reduced diameter. The reduced diameter of the armatureportion 62 results in less fluidic resistance, because the armature hasless surface area in contact with the infusion medium and displaces lessvolume of the infusion medium during actuator movement. Alternatively,instead of reducing the armature diameter, the diameter dimensions ofthe coil, coil cup member and housing may be increased relative to thediameter of the armature portion 62, to increase electromagnetic powerapplied to the armature. However, such an alternative embodiment mayresult in increased power consumption and increased dimensions of thepump mechanism. Thus, embodiments employing a reduced diameter armatureportion 62 may be preferred in implant environments, in which minimizingsize and maximizing power usage efficiency are typically important.

[0101] According to further embodiments of the present invention, thearmature portion 62 of the actuator 36 may be manufactured from anysuitable material, including materials having a low magneticpermeability. According to these embodiments, as shown in FIGS. 14A, 14Band 15, armature portion 62 of the actuator 36 may be formed with acavity 117 into which a material 119 may be placed. Material 119 may beany suitable material having a relatively high magnetic permeabilitysuch as, but not limited to, ferrous materials such as S44700 stainlesssteel or the like. A cover 121 made from a material such as, but notlimited to, a foil material, may then be placed over the cavity 117 toprovide a cover for material 119. FIG. 14A shows armature portion 62,material 119 and cover 121 in an unassembled state. FIG. 14B showsarmature portion 62, material 119 and cover 121 in an assembled state.FIG. 15 shows an assembled actuator 36 (including the armature portion62 and the piston portion 64) having a cavity 117 into which a material119 is placed and covered with cover 121, according to an embodiment ofthe present invention. The material 119 may be chosen to have anysuitable dimensions.

[0102] By providing a cavity in the armature portion 62 of the actuator36 in which to place and cover the relatively high magnetic permeabilitymaterial, contact between the relatively high magnetic permeabilitymaterial and the infusion medium is minimized. The relatively highmagnetic permeability material provides a flux path for electromagneticflux, so that the remainder of the armature portion 62 need not do so.Thus, the remainder of the armature portion 62 may be manufactured fromany suitable biocompatible and infusion medium compatible material,having no or low magnetic permeability such as, but not limited to,titanium, stainless steel (which may be ferritic or non-ferritic),biocompatible plastic, ceramic, glass or the like.

[0103] When assembled (as shown in FIGS. 3A-D and 4A-D), the armatureportion 62 of the actuator member 36 resides adjacent the open end ofthe coil cup member 32 and the piston portion 64 of the actuator member36 extends into the piston channel 44 of the housing member 30. Asdescribed above, the armature portion 62 of the actuator member 36includes a magnetically permeable material. This allows the armature toelectromagnetically cooperate with the coil cup member 32 and form aflux path, upon electrical energization of the coil 34.

[0104] More specifically, the armature portion 62 is provided with anannular inner pole surface 65 and an annular outer pole surface 66. Inthe illustrated embodiments, the annular pole surfaces 65 and 66 areraised relative to the rest of the armature portion 62, for example, toallow for a greater amount of magnetically permeable material to bepresent at the pole locations. However, in other embodiments, the polesurfaces may be in plane with the rest of the armature portion orrecessed relative to the rest of the armature portion.

[0105] A simplified, cross-sectional diagram of the coil cup member 32and the actuator member 36 illustrated in FIG. 3A, in their assembledorientation, is shown in FIG. 9. As described in more detail below, theinner and outer pole surfaces 65 and 66 of the armature portion 62 alignwith the inner and outer pole surfaces 54 and 59 of the coil cup member32 to allow a flux path F to be formed, when the coil 34 is energized.Upon energization of the coil 34, the flux path F is formed through theouter peripheral wall 56 of the coil cup member 32 and across a gapbetween the outer pole surface 59 of the coil cup member 32 and theouter pole surface 66 of the armature portion 62. The flux path Fcontinues through the armature portion 62, across the gap between theinner pole surface 65 of the armature portion 62 and the inner polesurface 54 of the coil cup member 32. The circuit of the flux path F iscompleted through the hub portion 51 and backiron 57 of the coil cupmember 32, and back to the outer peripheral wall 56 of the coil cupmember 32. Although not described in detail, embodiments of the presentinvention illustrated in FIGS. 3B-D operate in a similar manner to thatdescribed for the embodiment illustrated in FIG. 3A.

[0106] As shown in FIG. 9, by employing a coil cup member 32 with ashelf 58 extending toward the hub 51, the outer pole 66 of the armatureportion 62 need not extend to the outer wall 56 to provide the flux pathF. Instead, a portion of the flux path F can be provided through theshelf 58. In this manner, the diameter D of the armature portion 62 maybe minimized, for example, to simplify manufacturing processes, reducestirring of infusion media during actuator movement and/or make moreefficient use of power. Alternatively, the shelf 58 may be employed toallow the diameter of the coil cup member 32 to be increased, withoutrequiring a like increase in the diameter of the armature portion 62.

[0107] In the embodiment shown in FIG. 9, the relative dimensions of thearmature portion 62, coil cup member 32 and shelf 58 are selected suchthat the outer pole 66 of the armature portion 62 overlaps a portion ofthe shelf 58. A gap is provided between the outer pole 66 of thearmature portion 62 and the shelf 58. Similarly, a gap is providedbetween the inner pole 65 of the armature portion 62 and the inner polesurface 54 of the coil cup member 32.

[0108] In some embodiments, the armature portion 62 and/or the coil cupmember 32 may be configured such that the gap between the outer polesurface 66 of the armature portion 62 and the outer pole surface 59 ofthe coil cup member 32 is greater than the gap between the inner polesurface 65 of the armature portion 62 and the inner pole surface 54(FIG. 7A) of the coil cup member, when the actuator is in the retractedposition shown in FIGS. 3A-D. A greater outer pole spacing, relative tothe inner pole spacing, can result in reduced residual flux that couldotherwise cause the armature to stick in the forward position (the FIGS.4A-D position). In addition, a greater outer pole spacing reduces thesqueezing effect on infusion medium between the outer pole 66 of thearmature portion 62 and the shelf 58, as the armature 42 moves towardthe forward position during actuation of the pump mechanism.

[0109] As described in more detail below, the energization of the coil34 creates an electromagnetic force on the armature portion 62 of theactuator 36, to draw the armature portion 62 toward the coil cup member32 (i.e., to close the gaps between the inner pole surfaces 54 and 65and between the outer pole surfaces 59 and 66). By drawing the armatureportion 62 of the actuator member 36 toward the coil cup member 32, thepiston portion 64 of the actuator member 36 is forced further into thepiston channel 44, toward the outlet chamber of the housing member 30.This action effects a forward stroke of the drive mechanism 20, as shownin FIGS. 4A-D. Upon sufficient de-energization of the coil 34, theactuator member 36 is forced toward a retracted position, as shown inFIGS. 3A-D, for example, by the force of a spring 68, a magnet (notshown) or both.

[0110] The actuator spring 68 in the illustrated embodiment comprises acoil spring disposed around the piston portion 64 of the actuator member36, adjacent the armature portion 62 of the actuator member 36. One endof the coil spring abuts the armature portion 62 of the actuator, whilethe opposite end of the coil spring abuts a shoulder 70 in the pistonchannel 44 of the housing member 30. In this manner, the actuator spring68 imparts a spring force between the housing member 30 and the actuatormember 36, to urge the actuator member 36 toward its retracted positionshown in FIGS. 3A-D.

[0111] In the illustrated embodiment, by using a coil spring 68 locatedaround and coaxial with the piston portion 64 and disposed partiallywithin the piston channel 44, the actuator spring may have minimal or nocontribution to the overall thickness dimension of the drive mechanism.However, in other embodiments, actuator springs may have other suitableforms and may be located in other positions suitable for urging theactuator toward its retracted position shown in FIGS. 3A-D. The actuatorspring 68 is preferably made of a biocompatible and infusion mediumcompatible material that exhibits a suitable spring force such as, butnot limited to, titanium, stainless steel, MP35N cobalt steel or thelike. In further embodiments, a magnet may be arranged to provide areturn force on the actuator, either in addition to or as an alternativeto the actuator spring 68, to return the actuator to its retractedposition. An example of a magnet arranged for providing a return forceon an actuator is described in U.S. patent application Ser. No.10/033,724.

[0112] Cover Member for Drive Mechanism

[0113] The cover member 38 of the drive mechanism 20 attaches to thehousing member 30, to cover the open side of the housing member, thearmature portion 62 and the barrier 61. The cover member 38 ispreferably made of a generally rigid, biocompatible and infusion mediumcompatible material, having a relatively low magnetic permeability(being relatively magnetically opaque) such as, but not limited to,titanium, stainless steel, biocompatible plastic, ceramic, glass or thelike.

[0114] The cover member 38 defines an interior volume 72 between thebarrier 61 and the inner surface of the cover member. The armatureportion 62 of the actuator member 36 resides within the interior volume72 when the cover is attached to the housing, as shown in FIGS. 3A-D and4A-D. As described below, the armature portion 62 of the actuator 36 ismoveable in the axial direction A within the volume 72, between aretracted position shown in FIGS. 3A-D and a forward stroke positionshown in Figures A-D. This movement is created by the action ofelectromagnetic force generated when a current is passed through thecoil 34 and by the mechanical return action of the actuator spring 68.

[0115] An adjusting plunger 74 may be located within the cover member38, for contacting the armature portion 62 of the actuator 36, when thearmature portion 62 is in the fully retracted position shown in FIGS.3A-D. The adjusting plunger 74 may be used to set the retracted positionof the armature portion 62. A seal may be disposed between the plunger74 and the cover member 38, for example, but not limited to, a siliconrubber sealing ring. In further embodiments, a flexible diaphragm 76(such as, but not limited to, a thin titanium sheet or foil) may becoupled to the inside surface of the cover member 38 and sealed aroundthe opening through which the plunger 74 extends. The diaphragm willflex to allow the plunger to define an adjustable retracted positionand, yet, provide sealing functions for inhibiting leakage at theinterface between the plunger 74 and the cover member 38. In furtherembodiments, once a proper armature position is set, the plunger may befixed in place with respect to the cover member, for example, byadhering the plunger to the cover member with one or more welds,adhesives or other securing methods.

[0116] The cover member 38 includes the inlet 26 of the drive mechanism,which has an inlet opening 78 in fluid flow communication with theinterior volume 72. The inlet opening 78 connects in fluid flowcommunication with the reservoir of the infusion device 10 (FIG. 1), toreceive infusion medium from the reservoir. Connection of the inletopening 78 and the reservoir may be through suitable conduit (notshown), such as tubing made of or coated with suitable infusion mediumcompatible material, including, but not limited to titanium, stainlesssteel, biocompatible plastic, ceramic, glass or the like. In a furtherembodiment, the tubing is made of or coated with a material selected tobe compatible with a variety of infusion media, such as, but not limitedto titanium, titanium alloy, stainless steel, or the like.

[0117] Piston Channel and Outlet Chamber for Drive Mechanism

[0118] As shown in FIGS. 3A-D and 4A-D, the piston portion 64 of theactuator member 36 extends through the axial piston channel 44 in thehousing member 30, toward the outlet chamber 48 at the end of the pistonchannel 44. The channel 44 has an inside diameter which is larger thanthe outside diameter of the piston portion 64. As a result, an annularvolume is defined between the piston portion 64 and the wall of thepiston channel 44, along the length of the piston channel 44. Infusionmedium may flow through the annular volume, from the volume 72 withinthe cover member 38 to a piston chamber 80 located between the free endof the piston portion 64 and a valve Member 82 of a valve assembly 84.

[0119] In some example embodiments of the invention, the radial spacingbetween the piston portion 64 and the wall of the piston channel 44 isselected to be large enough to provide a suitable flow of infusionmedium toward the pumping chamber 80 to refill the pumping chamber 80(during a return stroke of the piston portion), but small enough tosufficiently inhibit back flow of medium from the pumping chamber 80(during a forward stroke of the piston portion).

[0120] The actual radial spacing between the piston portion 64 and thewall of the channel 44 to achieve such results depends, in part, on theoverall dimensions of those components, the pressure differentialscreated in the mechanism and the viscosity of the infusion medium. Forexample, the radial spacing may be selected such that the volume ofmedium for refilling is between about 1 and 4 orders of magnitude (and,more preferably, about 2 orders of magnitude) greater than the volume ofmedium that backflows through the space. Alternatively, or in addition,the radial spacing may be defined by the ratio of the diameter D_(P) ofthe piston portion 64 the diameter D_(C) of the channel 44, where theratio D_(P)/D_(C) is preferably within a range of about 0.990 to about0.995. As a representative example, a total spacing of about 400 to 600micro-inches or less and, preferably, an average radial gap of about 250micro-inches annularly around the piston portion 64 may be employed. Infurther embodiments described below with reference to FIGS. 10-12, otherrelative dimensions between the piston portion and pumping channel maybe employed.

[0121] The valve assembly 84 in the embodiment of FIGS. 3A-D and 4A-Dincludes the valve member 82, a valve spring 83 and support ring 85. Thevalve member 82 is located within the outlet chamber 48 and, as shown inFIGS. 3A-D, is positioned to close the opening between the axial pistonchannel 44 and the outlet chamber 48, when the actuator member 36 is inthe retracted position. In FIGS. 4A-D, the valve member 82 is positionedto open a flow passage between the axial piston channel 44 and theoutlet chamber 48. The valve spring 83 is located within the outletchamber 48, to support the valve member 82. The spring 83 imparts aspring force on the valve member 82, in the direction toward piston 64,urging the valve member 82 toward a closed position, to block theopening between the axial channel 44 and the outlet chamber 48.

[0122] The valve member 82 and the support ring 85 are preferably madeof a generally rigid, biocompatible and infusion medium compatiblematerial, such as, but not limited to, titanium, stainless steel,biocompatible plastic, ceramic, glass, gold, platinum or the like. In afurther embodiment, the valve member and ring are made of or clad with amaterial selected to be compatible with a variety of infusion media,such as, but not limited to titanium or titanium alloy, or the like.

[0123] A layer of silicon rubber or other suitable material may beattached to the rigid valve member material, on the surface facing thechannel 44, to help seal the opening to the channel 44 when the valvemember is in the closed position shown in FIGS. 3A-D. Variousalternative valve assembly configurations may be employed withembodiments of the present invention, including, but not limited to suchconfigurations as described in co-pending U.S. patent application Ser.No. 10/033,722.

[0124] The valve spring 83 is preferably made of a biocompatible andinfusion medium compatible material that exhibits a suitable springforce such as, but not limited to, titanium, stainless steel, MP35Ncobalt steel or the like. In a further embodiment, the spring is made ofor clad with a material selected to be compatible with a variety oftypes of infusion media, such as, but not limited to titanium, titaniumalloy, stainless steel, or the like.

[0125] In the illustrated embodiment, the outlet chamber 48 comprises acavity in the bottom of the housing 30, as shown in FIGS. 3A-D and 4A-D.The outlet chamber cavity 48 may be provided in flow communication withan outlet 28 (FIG. 2), through a flow passage (not shown). The outletflow passage may include one or more accumulator cavities provided withaccumulators, as described in the above-referenced U.S. patentapplication Ser. No. 10/033,722, for example, to help stabilize the flowrate of the drive mechanism, help provide a relatively constant outputpressure during drive operations, and minimize backflow down axialchannel 44.

[0126] Manufacturing Process for Drive Mechanism

[0127] A drive mechanism as shown in FIGS. 3A-D and 4A-D may beconstructed by providing components as shown in FIG. 5 and assemblingthe components in any suitable sequence. The components may be madeaccording to any suitable process including, but not limited to molding,machining, extruding, sintering, casting, combinations thereof or thelike.

[0128] The coil 34 may be inserted into the annular interior of the coilcup member 32, with the coil leads extended through a coil lead opening60 in the coil cup. The coil may be impregnated or partially impregnatedwith a fill material of epoxy or the like, for adhering the coil to thecoil cup and for sealing or partially sealing the coil. The fillmaterial may also be used to adhere the barrier plate 61 to the coilmembers, to avoid warping or bulging of the barrier plate afterassembly.

[0129] The coil cup member 32 and coil 34 may be inserted into theinterior 40 of the housing member 30, with the coil leads or connectors(which may be wire leads or flexible conductive tabs) extending througha coil lead opening 46 in the housing member 30. In preferredembodiments, the coil cup and housing members are configured to providea tight, friction fit therebetween, without requiring additional meansof adhering the two components together. In other embodiments, the coilcup and housing members may be coupled together by any suitable adhesivematerial or other adhering methods, including, but not limited towelding, brazing, of the like.

[0130] The barrier 61 may be placed over the coil, coil cup and housingsub-assembly. The barrier 61 may be adhered to the housing by one ormore adhering points or continuously along the circumference of thebarrier 61, with any suitable adhesive material or other adheringmethods, including, but not limited to welding, brazing, soldering orthe like. Alternatively, or in addition, the barrier 61 may be held inplace by a shoulder portion of the cover member 38. In addition, asnoted above, the barrier 61 may be adhered to the coil 34 by fillmaterial in the coil. In preferred embodiments, the barrier 61 is heldin a generally flat relation relative to the coil cup member and coil.To enhance this flat relation, the coil cup and housing members mayassembled together and then machined to planarize the barrier contactsurfaces, prior to inserting the coil in the coil cup and prior toadding fill material to the coil.

[0131] Once the barrier 61 is placed over the coil, coil cup and housingmembers, the actuator member 36 may be added to the sub-assembly. First,however, the actuator spring 68 is placed around the piston portion 64,adjacent the armature portion 62 of the actuator member 36. Then thefree end of the piston portion 64 is inserted into the axial channel 44of the housing member 30, with the armature end of the actuator member36 arranged adjacent the barrier 61.

[0132] The cover member 38 may then be disposed over the armature end ofthe actuator member 36 and secured to the housing member 30. Inpreferred embodiments, the cover member 38 is adhered to the housingmember 30 by one or more adhering points or continuously along thecircumference of the cover member 38, with one or more welds or anyother suitable adhering methods, including, but not limited to adhesivematerials, brazing or the like.

[0133] The valve side of the drive mechanism may be assembled before orafter the above-described components are assembled. On the valve side ofthe drive mechanism, the valve member 82 is disposed within the outletchamber cavity 48 of the housing member 30. The valve spring 83 and ring85 are disposed within the outlet chamber cavity 48, adjacent the valvemember 82. Any suitable number of accumulators may be placed within eachof the accumulator cavities (not shown). A valve cover 86 may then beplaced over the outlet chamber cavity 48 and accumulator cavities. Thevalve cover 86 may be adhered to the housing member 30 by one or moreadhering points or continuously along the circumference of the valvecover, with one or more welds or any other suitable adhering methods,including, but not limited to adhesive materials, brazing or the like.

[0134] The volume of the pumping chamber 80, the compression of theactuator spring 68 and the position of the actuator 36 in the retractedposition shown in FIGS. 3A-D may be adjusted by the adjusting theposition of the adjusting plunger 74. Adjustments of the plunger 74 maybe made during manufacture and the adjusted position may be fixed bywelding or otherwise adhering the plunger 74 in the adjusted positionduring manufacture. In other embodiments, the plunger 74 is not set andwelded during manufacture, to allow adjustment of plunger 74 aftermanufacture.

Operation of Drive Mechanism

[0135] In operation, the drive mechanism 20 employs electromagnetic andmechanical forces to move between retracted (FIGS. 3A-D) and forward(FIGS. 4A-D) positions, to cause infusion medium to be drawn into anddriven out of the mechanism in a controlled manner. In the retractedposition, the spring 68 urges the actuator 36 toward its retractedposition shown in FIGS. 3A-D. When the coil 34 is energized to overcomethe spring force of spring 68, the actuator 36 moves to its forwardstroke position shown in FIGS. 4A-D. The movement of the actuatorbetween retracted and forward positions creates pressure differentialswithin the internal chambers and volumes of the drive mechanism 20 todraw medium into the inlet 26 and drive medium out the outlet 28.

[0136] More specifically, when the coil 34 is de-activated (notenergized or not energized in a manner to overcome the spring force ofspring 68), the actuator 36 is held in its retracted position (FIGS.3A-D) under the force of the spring 68. When the coil is de-activatedimmediately following a forward stroke, the spring 68 moves the actuator36 to the retracted position of FIGS. 3A-D, from the forward positionshown in FIGS. 4A-D.

[0137] As the actuator 36 retracts, the piston portion 64 of theactuator is retracted relative to the valve member 82, such that apumping chamber 80 volume is formed or expanded between the end of thepiston portion 64 and the valve member 82. The formation or expansion ofthe pumping chamber 80 volume creates a negative pressure which drawsinfusion medium from the volume 72 of the cover member 38, through theannular space between the piston portion 64 and the wall of the pistonchannel 44, and into the pumping chamber 80. While not shown in FIGS.3A-D, other embodiments (such as shown in FIGS. 10-12) may include oneor more channels through the piston portion 64, to provide one or moreadditional flow paths to the pumping chamber 80.

[0138] In the retracted position, a gap is formed between each of theannular inner and outer pole surfaces 54 and 59 on the coil cup member32 and a respective annular surfaces of the inner and outer polesurfaces 65 and 66 on the armature portion 62 of the actuator member 36.In particular, with reference to FIGS. 3A-D, gaps are formed between theannular pole surfaces of the coil cup member 32 and the armature portion62 of the actuator member 36.

[0139] When the coil 34 is energized (or energized sufficiently toovercome the spring force of spring 68), the actuator member 36 isforced in the direction to close the gaps between the pole surfaces andmoves to its forward position (FIGS. 4A-D) under the influence ofelectromagnetic flux generated by the energized coil. In particular, thecoil 34 may be energized by passing an electrical current through thecoil conductor to create electromagnetic flux. The electromagnetic fluxdefines a flux path F as described above with respect to FIG. 9. Theelectromagnetic flux provides an attraction force between the annularpole surfaces 54 and 59 of the coil cup member 32 and the annular polesurfaces 65 and 66 of the armature portion 62 of the actuator member 36,to draw the armature portion 62 toward the coil cup member 32.

[0140] As the armature portion 62 of the actuator member 36 is drawntoward the coil cup member 32, the piston portion 64 of the actuatormember 36 is moved axially through the channel 44, in the directiontoward the outlet chamber 48. With the coil energized, the pistonportion 64 continues to move under the action of the armature, until amechanical stop is reached, for example, mechanical contact of thearmature portion 62 of the actuator 36 with the barrier 61, a portion ofthe housing member 30 or cover member 38. In other embodiments, themotion may continue until the return force of the spring 68 and fluidpressure inhibits any further forward motion from the electromagneticforce of the energized the coil.

[0141] The movement of the piston portion 64 towards the stopping pointreduces the volume of the pumping chamber 80 and increases the pressurewithin the piston chamber until the pressure is sufficient to overcomethe force of the valve spring 83. As the valve spring force is overcomeby the pressure within the piston chamber, the valve member 82 is movedtoward an open position, away from the opening between the pumpingchamber 80 outlet chamber 48. When the valve member 82 is in the openposition, medium is discharged through the outlet chamber 48 and,eventually, through outlet 28 (FIG. 2). When the coil is deactivated andthe piston portion 64 is moved back to its retracted position, thepressure in the pumping chamber 80 reduces and the valve member 82 isreseated under the action of the valve spring 83. This inhibits fluidfrom flowing back into the drive mechanism, through the outlet. Inaddition, a negative pressure is created in the pumping chamber 80 todraw medium into the chamber for the next forward stroke, as describedabove.

[0142] In this manner, energization of the coil 34 to move the actuatormember 36 from its retracted position (FIGS. 3A-D), to its forwardposition (FIGS. 4A-D), causes a measured volume of medium to bedischarged from the outlet. As described above, when the coil 34 isde-energized, the actuator member 36 is returned to the retractedposition (FIGS. 3A-D) under the force of spring 68 and an additionalvolume of medium is drawn into the pumping chamber 80 for the nextdischarging operation. Accordingly, the coil 34 may be energized andde-energized by a controlled electronic pulse signal, where each pulsemay actuate the drive mechanism 20 to discharge a measured volume ofmedium. In preferred embodiments, the coil 34 may be electricallycoupled to an electronic control circuit (not shown) to receive anelectronic pulse signal from the control circuit for example, inresponse to a sensor signal, timer signal or other control signal inputto the control circuit.

[0143] In preferred embodiments, when the piston motion is stopped atthe end of the forward stroke, the valve-facing end of the pistonportion 64 is in close proximity to the valve member 66, for example,spaced from the valve member 82 by no more than about ten percent (10%)of the piston stroke. In further embodiments, the valve facing end ofthe piston portion 64 is in contact with the valve member 82, at the endof the forward stroke. In this manner, gas that may be present in theinfusion medium is less likely to accumulate within the pumping chamber80. More specifically, in some operational contexts, infusion medium maycontain gas in the form of small bubbles that may migrate into thepumping chamber 80 during filling of the piston chamber. As gas issignificantly more compressible than liquid, too much gas within thepumping chamber may adversely affect the ability of the drive mechanismto self prime.

[0144] In yet another embodiment the piston portion 64 may contact thevalve member 82 at the end of the forward stroke and push the valvemember 82 open. In this embodiment, it is less likely that gas will betrapped between the piston portion 64 and the valve member 82, and morelikely that the chamber will be purged of gas.

[0145] Further Drive Mechanism Embodiments

[0146] In the embodiments described above, movement of the actuator 36to the retracted position (FIGS. 3A-D) causes the piston portion 64 ofthe actuator to retract, such that a pumping chamber 80 volume is formedor expanded between the end of the piston portion 64 and the valvemember 82. The formation or expansion of the pumping chamber 80 volumecreates a negative pressure which draws infusion medium from the volume72 of the cover member 38, through the annular space between the pistonportion 64 and the wall of the piston channel 44, and into the pumpingchamber 80.

[0147] The rate at which the infusion medium fills the pumping chamber80 can depend upon various factors, including the viscosity of theinfusion medium and the width of the

[0148] annular space between the piston portion 64 and the wall of thepiston channel 44. To accommodate a greater variety of infusion mediaand, thus, a greater range of viscosities, embodiments of the inventionmay employ a piston portion 64 and piston channel 44 configured toimprove the flow of an infusion medium into the pumping chamber 80. Suchconfigurations may include one or more of the features described belowwith respect to FIGS. 10-12.

[0149]FIG. 10 shows an embodiment of an actuator member 36′ having anarmature portion 62′ and a piston portion 64′, similar in many respectsto the armature portion 62 and piston portion 64 of the actuator member36 described above. However, the actuator member 36′ is configured witha central channel 90 extending through the armature portion 62′ and theaxial length of the piston portion 64′. The channel 90 has openings 92and 93 on the armature and piston ends of the actuator member 36′. Whenthe actuator member 36′ is employed in a pump drive mechanism 20 asshown in FIGS. 3A-D and 4A-D, the channel 90 allows the infusion mediumto flow from the cover volume 72, through the piston portion 64′ andinto the pumping chamber 80. Thus, as the actuator member 36′ movestoward a retracted position (the FIGS. 3A-D position of the actuatormember), fluidic infusion medium flows through the channel 90 and intothe pumping chamber 80.

[0150] A valve structure 94 may be provided to control the flow of fluidthrough the channel 90. For example, a valve structure 94 may beconfigured to restrict or inhibit a reverse flow of infusion medium fromthe pumping chamber 80 and back through the channel 90, toward the covervolume 72, during forward strokes of the actuator. In one embodiment,the valve structure may comprise a ball-shaped plug located in a taperedvolume, for selectively blocking the flow of infusion medium through thechannel 90, as shown in FIG. 10. In other embodiments, other suitablevalve configurations may be employed, including, but not limited to acone-shaped plug in a larger cone-shaped volume, or the like.

[0151] The valve structure 94 may be located within the channel 90, forexample, adjacent the piston chamber opening 93 of the channel 90.Alternatively, the valve structure 94 may be located in other suitablepositions along the length of the channel 90. In further embodiments,the valve structure may include a ball (or other shaped plug) locatedwithin the pumping chamber 80, for selectively blocking the opening 93of the channel 90. In such further embodiments, the opening 93 of thechannel 90 may be shaped to cooperate with the shape of the ball (orother shaped plug), to provide a sealing or partial sealing functionagainst back flow of the infusion medium. Thus, for example, the opening93 may be tapered inward, cone-shaped or the like, to provide a seat forthe ball (or other shaped plug) within the pumping chamber 80. In yetfurther embodiments, multiple valve structures may be located, forexample, along the length of the channel 90, at the opening 92, at theopening 93 and/or within the pumping chamber 80, as described above.

[0152] During each forward stroke of the actuator member 36′, the valvestructure 94 closes and the infusion medium is restricted or inhibitedfrom flowing from the pumping chamber 80, through the channel 90, towardthe cover volume 72, for example. However, as the actuator member 36′ ismoved back toward a retracted position, the valve structure 94 opens andallows the infusion medium to flow from the cover volume 72, through thechannel 90 and into the pumping chamber 80. In this manner, the channel90 and valve structure 94 provide a controlled flow path, for thecommunication of infusion medium into the pumping chamber 80. Moreover,the channel 90 and valve structure 94 may be readily configured withsufficient channel width to allow sufficient filling of the pumpingchamber 80 with any one of a variety of infusion media (and, thus, avariety of infusion medium viscosities).

[0153] The flow path provided by the channel 90 may be employed incombination with an annular space (described above) between the pistonportion 64′ and the wall of the piston channel 44, to communicateinfusion medium to the pumping chamber 80. In further embodiments, thechannel 90 may provide the primary or sole flow path for communicationof infusion medium into the pumping chamber 80. In such furtherembodiments, the annular space between the piston portion 64′ and thewall of the piston channel 44 may be minimized.

[0154] While embodiments described above employ a single piece actuatormember 36′, further embodiments of an actuator with a central channel 90may be employed with multi-piece actuator embodiments, such as the2-piece actuator member described in U.S. patent application Ser. No.10/033,722, as the “second drive mechanism embodiment and operation.” Insuch embodiments, the armature portion of the actuator member isseparable from the piston portion of the actuator member. For example,the 2-piece actuator member 36″ shown in FIG. 11 includes an armatureportion 62″ and a piston portion 64″, configured as two separablepieces.

[0155] A channel 90, as described above, is provided through the pistonportion 64″, but need not be provided through the armature portion 62″of the actuator member 36″. A valve structure 94, as described above,may be provided in the piston portion 64″. Alternatively, or inaddition, a valve structure located in the pumping chamber 80 and/ormultiple valve structures as also described above, may be employed withthe 2-piece actuator embodiment of FIG. 11.

[0156] In embodiments as shown in FIGS. 12 and 13, an alternative valvestructure may be employed to control a flow of infusion medium from thechannel 90 of the piston to the pumping chamber 80. For example, asshown in FIG. 12, actuator member 36′″ may include a valve structure 96.Valve structure 96 may be configured to restrict or inhibit a reverseflow of infusion medium from the pumping chamber 80 and back through thechannel 90, toward the cover volume 72, during forward strokes of theactuator (FIGS. 4A-D). A more detailed view of one embodiment of valvestructure 96 is shown in FIG. 13.

[0157] As shown in FIG. 13, one embodiment of the valve structure 96 maycomprise a cap 103, a seat 105, and a washer 107. According toembodiments of the present invention, seat 105 has a generallyfrusto-conical shape. However, any suitable shape may be used,including, but not limited to, flat and radiused. The tapered end ofseat 105 is coupled to piston portion 64′″. In one embodiment, seat 105is integral with piston portion 64′″. Piston portion 64′″ may be formedto include indented area 109 for receiving a catch of cap 103. Cap 103may be placed over the end of piston portion 64′″ closest to the pistonchamber 80 such that the catch snaps into indented area 109 to securecap 103 to piston portion 64′″. Cap 103 and seat 105 may be made fromany suitable biocompatible material, including, but not limited to,metal and plastic. In one embodiment, cap 103 is made from polysulfone.

[0158] Washer 107 is located between cap 103 and seat 105 to provide asealing function for inhibiting leakage at the interface between seat105 and washer 107 during forward strokes of the actuator. In thismanner, reverse flow of infusion medium is inhibited during forwardstrokes of the actuator. Cap 103 may include an indentation for seatingwasher 107. Washer 107 may be press fit into the indentation and/or maybe secured within the indentation by means of a suitable adhesive or thelike. Washer 107 may be made from any suitable biocompatible material,including, but not limited to, silicone rubber.

[0159] During a forward stroke, seat 105 is sealed against washer 107due to pressure created in pumping chamber 80, and space 111 is formedby the upward movement of the catch within indented area 109. However,during reverse strokes, washer 107 and seat 105 separate from oneanother due to suction (vacuum) created in pumping chamber 80. Thus,when piston portion 64′″ is in a reverse stroke, suction is applied tocap 103 such that cap 103 moves in a direction opposite to the upwardmovement of piston portion 64′″. Space 111 allows catch to move downwardwithin indented area 109 until the catch comes to a stop against thebottom shoulder of indented area 109. The separation of washer 107 andseat 105 allows flow of infusion medium from cover volume 72 through thechannel 90, into pumping chamber 80 during reverse strokes. In oneembodiment, space 111 may be equal to approximately 0.002 inches orabout 20% of the stroke of piston portion 64′″. Other suitabledimensions may be used in other embodiments of the valve structure 96.

[0160] In yet further embodiments, the annular space between the pistonportion of the actuator member 36 and the wall of the piston channel 44may be increased relative to the above-described embodiments, toincrease the rate of flow of infusion medium from the cover volume 72,into the pumping chamber 80. For example, as shown in FIG. 12, anactuator member 36′″ may be provided with a piston portion 64′″ having areduced diameter relative to the actuator members shown in theabove-described embodiments. In such embodiments, the rate at which agiven infusion medium may flow through the annular space between thepiston portion 36′″ and the piston channel 44 is increased (relative toembodiments employing a larger diameter piston portion). Accordingly,the rate of filling of the piston chamber may be increased, for example,to accommodate a greater variety of infusion media.

[0161] Alternatively, or in addition to employing an actuator member36′″ having a relatively small diameter piston portion 64′″, thediameter of the piston channel 44 may be increased, relative to theabove-described embodiments. By employing a relatively small diameterpiston portion 64′″ and/or a relatively large diameter piston channel44, the annular space between the piston portion 64′″ and the pistonchannel 44 (and, thus, the rate at which a given infusion medium mayflow through the annular space) may be similarly increased.

[0162] Various features that may be employed in infusion drivemechanisms for improving operation with a any one of a variety ofinfusion media are described herein in connection with the embodiment ofFIGS. 10-12. Further features that may be employed for improvingoperation with any one of a variety of infusion media are describedherein in connection with FIGS. 3-9. However, it is contemplated that,where possible, features described in connection with one embodiment maybe employed in the other embodiment. For example, the armature and coilcup configurations of FIGS. 3-9 may be employed in combination with oneor more of the channel 90, valve configurations 94 and increased annularspacing between the piston portion and piston channel described abovewith respect to FIGS. 10-12. Moreover, embodiments of FIGS. 3-12 may beemployed with single-piece actuator configurations or multi-pieceactuator configurations.

[0163] While drive mechanism embodiments described above employ acoaxial arrangement of the coil, piston channel and piston, otherembodiments may employ a piston and piston channel located between, butnot coaxial with, a plurality of spaced coils. For example three coilsmay be located in a spaced relation at three respective corners of atriangle, with the piston channel and piston located in the center ofthe triangle (surrounded by the three locations of the coils), and withthe piston axis parallel to the axes of the coils. In furtherembodiments more than three coils may be located at discrete positionsspaced around the piston (at locations surrounding the piston),preferably, equally spaced from the piston or otherwise arranged toprovide approximately equal forces on the piston.

[0164] The foregoing description of the preferred embodiment of theinvention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching.

What is claimed is:
 1. A coil cup composed of a magnetizable material,the coil cup comprising: a generally annular inner wall having one enddefining an inner pole surface of the coil cup; a generally annularouter wall having a first inner diameter and a first outer diameter, theouter wall having a generally annular shelf portion extending from theouter wall towards the inner wall, the shelf portion having a secondinner diameter and a second outer diameter, the second inner diameterbeing smaller than the first inner diameter, the shelf portion having asecond end defined by the second inner and outer diameters, the secondend defining at least a portion of an outer pole surface of the coilcup; and a generally annular interior between the inner and outer walls,the annular interior containing a coil.
 2. The coil cup recited in claim1, wherein the shelf portion has an angled edge.
 3. The coil cup recitedin claim 1, wherein the second outer diameter is equal to the firstouter diameter.
 4. A coil cup composed of a magnetizable material, thecoil cup comprising: a generally annular outer wall having one enddefining an outer pole surface of the coil cup; a generally annularinner wall having a first inner diameter and a first outer diameter, theinner wall having a generally annular shelf portion extending from theinner wall towards the outer wall, the shelf portion having a secondinner diameter and a second outer diameter, the second outer diameterbeing greater than the first outer diameter, the shelf portion having asecond end defining at least a portion of an inner pole surface of thecoil cup; and a generally annular interior between the outer and innerwalls, the annular interior containing a coil.
 5. The coil cup recitedin claim 4, wherein the shelf portion has an angled edge.
 6. The coilcup recited in claim 4, wherein the second inner diameter is equal tothe first inner diameter.
 7. A coil cup composed of a magnetizablematerial, the coil cup comprising: a generally annular outer wall havinga first inner diameter and a first outer diameter, the outer wall havinga generally annular outer shelf portion extending from the outer walltowards the inner wall, the outer shelf portion having a second innerdiameter and a second outer diameter, the second inner diameter beingsmaller than the first inner diameter, the outer shelf portion havingone end defined by the second inner and outer diameters, the one enddefining at least a portion of an outer pole surface of the coil cup; agenerally annular inner wall having a third inner diameter and a thirdouter diameter, the inner wall having a generally annular inner shelfportion extending from the inner wall towards the outer wall, the innershelf portion having a fourth inner diameter and a fourth outerdiameter, the fourth outer diameter being greater than the third outerdiameter, the inner shelf portion having a second end defining at leasta portion of an inner pole surface of the coil cup; and a generallyannular interior between the outer and inner walls, the annular interiorcontaining a coil.
 8. The coil cup recited in claim 7, wherein the outershelf portion has an angled edge.
 9. The coil cup recited in claim 7,wherein the inner shelf portion has an angled edge.
 10. The coil cuprecited in claim 7, wherein the second outer diameter is equal to thefirst outer diameter.
 11. The coil cup recited in claim 7, Wherein thefourth inner diameter is equal to the third inner diameter.
 12. A drivemechanism comprising: a piston channel; a coil surrounding the pistonchannel; a piston located within the piston channel and moveable axiallywithin the piston channel; a coil cup supporting the coil, the coil cupincluding: a generally annular inner wall having one end defining aninner pole surface of the coil cup; a generally annular outer wallhaving a first inner diameter and a first outer diameter, the outer wallhaving a generally annular outer shelf portion extending from the outerwall towards the inner wall, the outer shelf portion having a secondinner diameter and a second outer diameter, the second inner diameterbeing smaller than the first inner diameter, the outer shelf portionhaving a second end defined by the second inner and outer diameters, thesecond end defining at least a portion of an outer pole surface of thecoil cup; and a generally annular interior between the inner and outerwalls, the annular interior containing the coil; and an armaturedisposed adjacent the coil on one side of the piston channel thearmature having inner pole and outer pole surfaces for acting with theinner and outer pole surfaces of the coil cup to provide anelectromagnetic flux path upon electrical activation of the coil, theelectromagnetic flux path for drawing the armature towards the coil cupand for moving the piston axially within the piston channel.
 13. Thedrive mechanism recited in claim 12, wherein the inner wall has a thirdinner diameter and a third outer diameter, the inner wall having agenerally annular inner shelf portion extending from the inner walltowards the outer wall, the inner shelf portion having a fourth innerdiameter and a fourth outer diameter, the fourth outer diameter beinggreater than the third outer diameter, the fourth inner and outerdiameters defining a at least a portion of inner pole surface of thecoil cup.
 14. The drive mechanism as recited in claim 12, wherein theinner pole and outer pole surfaces of the armature have a generallyannular shape, the inner and outer pole surfaces of the armature eachbeing made of a magnetizable material, wherein the inner pole surface ofthe armature faces the inner pole surface of the inner wall of the coilcup, and the outer pole surface of the armature faces the outer polesurface of the coil cup.
 15. The drive mechanism recited in claim 14,wherein the armature has a generally annular shape and has an outerdiameter smaller than the first outer diameter of the outer wall of thecoil cup.
 16. The drive mechanism recited in claim 14, wherein thearmature has a generally annular shape and has an outer diameter smallerthan the first inner diameter of the outer wall of the coil cup.
 17. Thedrive mechanism recited in claim 14, wherein the armature has agenerally annular shape and has an outer diameter smaller than thesecond outer diameter of the outer shelf portion of the coil cup. 18.The drive mechanism recited in claim 14, wherein the outer pole surfaceof the armature faces only a portion of the outer shelf, the portion ofthe outer shelf being the portion having a diameter smaller than thefirst inner diameter of the outer wall of the coil cup.
 19. The drivemechanism recited in claim 14, wherein the outer pole surface of thearmature faces a portion of the outer shelf having a diameter smallerthan the first inner diameter of the outer wall of the coil cup andgreater than the second inner diameter of the outer shelf portion. 20.The drive mechanism recited in claim 12, wherein the outer shelf portionhas an angled edge.
 21. The drive mechanism recited in claim 13, whereinthe inner shelf portion has an angled edge.
 22. The drive mechanismrecited in claim 12, wherein the piston channel is surrounded by theinner wall and the piston channel is substantially coaxial with thecoil.
 23. The drive mechanism as recited in claim 12, wherein the pistonand armature are composed of a single, unitary structure.
 24. The drivemechanism as recited in claim 12, wherein the piston and armature arecomposed of separable structures and are moveable independent of eachother.
 25. A drive mechanism as recited in claim 12, further includingmeans for urging the armature and piston to move in an axial directionaway from the outlet chamber.
 26. A drive mechanism as recited in claim25, wherein the means for urging includes a spring.
 27. A drivemechanism as recited in claim 25, wherein the means for urging includesa magnet.
 28. A drive mechanism as recited in claim 12, furtherincluding: a valve member moveable between open and closed positions toselectively open and close one end of the piston channel to the outletchamber; and a valve spring for urging the valve member in the closedposition; wherein the valve member and valve spring are located withinthe outlet chamber.
 29. A drive mechanism as recited in claim 12,further including: a housing having a cavity containing the coil cup,the housing having a central channel that defines the piston channel,the housing having a further cavity disposed on one end of the pistonchannel, wherein the further cavity defines the outlet chamber; a valvemember moveable between open and closed positions to selectively openand close one end of the piston channel to the outlet chamber; and avalve spring for urging the valve member in the closed position; whereinthe valve member and valve spring are located within the further cavitydefining the outlet chamber.
 30. A drive mechanism as recited in claim29, wherein the piston is moveable in the axial direction of the pistonchannel between a retracted position and a forward position, wherein thevalve member is located in the closed position when the piston is in theretracted position and wherein the valve member is moved to the openposition when the piston is moved to the forward position.
 31. The drivemechanism as recited in claim 12, wherein the armature includes amagnetically permeable material.
 32. The drive mechanism as recited inclaim 12, wherein the armature includes at least one of a materialhaving no magnetic permeability and a material having a relatively lowmagnetic permeability, wherein the armature includes a cavity forholding another material having a relatively high magnetic permeability.33. The drive mechanism as recited in claim 32, wherein the at least oneof a material having no magnetic permeability and a material having arelatively low magnetic permeability is selected from the groupconsisting of titanium, stainless steel, biocompatible plastic, ceramic,and glass.
 34. The drive mechanism as recited in claim 32, wherein therelatively high magnetic permeability material includes a ferrousmaterial.
 35. The drive mechanism as recited in claim 32, wherein thecavity having the relatively high magnetic permeability material heldtherein is enclosed by a cover.
 36. The drive mechanism as recited inclaim 32, wherein the cover includes a foil material.
 37. A drivemechanism for delivery of infusion medium comprising: an inlet forreceiving infusion medium; a piston channel; a coil surrounding thepiston channel; a piston located within the piston channel, the pistonhaving a central channel extending through an axial length of the pistonand having openings at both ends of the piston, the central channel forconveying infusion medium received by the inlet, the piston beingmoveable axially within the piston channel to drive infusion medium intothe central channel; an armature disposed adjacent the coil, on one sideof the piston channel; an outlet chamber disposed adjacent the coil, onthe opposite side of the piston channel relative to the armature forreceiving infusion medium from the central channel; and an outlet inflow communication with the outlet chamber, for discharging infusionmedium from the outlet chamber.
 38. The drive mechanism recited in claim37, wherein the armature includes a central channel for conveyinginfusion medium received by the inlet, the central channel of thearmature being in fluid communication with the central channel of thepiston.
 39. The drive mechanism recited in claim 37, further includingat least one valve structure in fluid communication with the centralchannel of the piston, the at least one valve structure for controllinga flow of infusion medium from the central channel of the piston to theoutlet chamber.
 40. The drive mechanism recited in claim 39, wherein theat least one valve structure is configured to close during a forwardstroke of the piston and open during a reverse stroke of the piston. 41.The drive mechanism recited in claim 39, wherein the at least one valvestructure is configured to inhibit a reverse flow of infusion mediumfrom the outlet chamber to the central channel of the piston.
 42. Thedrive mechanism recited in claim 39, wherein at least a portion of theat least one valve structure is within the central channel of thepiston.
 43. The drive mechanism recited in claim 39, wherein at least aportion of the at least one valve structure is adjacent one of theopenings of the central channel of the piston.
 44. The drive mechanismrecited in claim 39, wherein the at least one valve structure includes aplug and a tapered volume for selectively inhibiting the reverse flow ofinfusion medium.
 45. The drive mechanism recited in claim 44, whereinthe plug is seated in the tapered volume.
 46. The drive mechanismrecited in claim 44, wherein the plug is in the central channel of thepiston and wherein at least one of the openings is shaped to include thetapered volume.
 47. The drive mechanism recited in claim 44, wherein theplug is a ball-shaped plug.
 48. The drive mechanism recited in claim 44,wherein the tapered volume is a cone-shaped tapered volume and whereinthe plug is a cone-shaped plug.
 49. The drive mechanism recited in claim39, wherein the valve structure includes: a seat having a centralchannel extending through an axial length of the seat and havingopenings at both ends of the seat, the central channel of the seat forconveying infusion medium, one end of the seat being coupled to one endof the piston such that one of the openings of the seat is in fluidcommunication with one of the openings of the piston; a seal having afirst side for moveably contacting the other one of the ends of the seatto inhibit flow of infusion medium from the other one of the openings ofthe seat; and a cap slideably connected to the one end of the piston,the cap having a first side for contacting a second side of the seal,the cap being slideable on the one end of the piston between a firstposition wherein the seal contacts the seat and a second positionwherein the seal does not contact the seat.
 50. The drive mechanismrecited in claim 49, wherein the cap includes a catch for slideablysecuring the cap to the one end of the piston and wherein the pistonincludes an indented area for receiving the catch.
 51. The drivemechanism recited in claim 49, wherein the cap is in the first positionwhen the piston is moving in one direction and in the second positionwhen the piston is moving in the opposite direction.
 52. The drivemechanism recited in claim 49, wherein the cap is slideably connected tothe end of the piston closest to the outlet chamber.
 53. The drivemechanism recited in claim 52, wherein the cap moves to the firstposition as a result of positive pressure in the outlet chamber.
 54. Thedrive mechanism recited in claim 52, wherein the cap moves to the secondposition as a result of a vacuum in the outlet chamber.
 55. The drivemechanism recited in claim 49, wherein the cap includes an indentationfor seating the seal.
 56. The drive mechanism recited in claim 49,wherein the seat has a generally frusto-conical shape.
 57. The drivemechanism recited in claim 49, wherein the cap is a plastic cap.
 58. Thedrive mechanism recited in claim 57, wherein the plastic cap is apolysulfone cap.
 59. The drive mechanism recited in claim 49, whereinthe cap is a metal cap.
 60. The drive mechanism recited in claim 49,wherein the seal is a washer.
 61. The drive mechanism recited in claim49, wherein the seal is a silicone rubber seal.
 62. The drive mechanismrecited in claim 37, further including a coil cup composed of amagnetizable material, the coil cup including: a generally annular innerwall having one end defining an inner pole surface of the coil cup; agenerally annular outer wall having a first inner diameter and a firstouter diameter, the outer wall having a generally annular shelf portionextending from the outer wall towards the inner wall, the shelf portionhaving a second inner diameter and a second outer diameter, the secondinner diameter being smaller than the first inner diameter, the shelfportion having a second end defined by the second inner and outerdiameters, the second end defining at least a portion of an outer polesurface of the coil cup; and a generally annular interior between theinner and outer walls, the annular interior containing the coil.
 63. Thedrive mechanism recited in claim 37, further including an annular spacebetween a wall of the piston channel and the piston located within thepiston channel, the annular space for conveying infusion medium receivedby the inlet.